Chemical Reactions and Equations

Chemical Reactions

• Chemical reactions involve reactants transforming into products.
• Reactants and products are identified in a chemical equation.
• The arrow indicates the transformation of reactants into products.

Valence

• Valence is the combining power of an element or the number of electrons an atom needs to gain, lose, or share to achieve a full or stable outer electron shell.
• The octet rule suggests atoms tend to gain, lose, or share electrons to have eight electrons in their outer shell.

Oxidation Number

• Oxidation state, or number, is assigned to elements in a molecule.
• Determine the oxidation states of all other elements in the molecule first, excluding the element of interest.
• The sum of all oxidation numbers equals zero, or the net charge on a molecule.

Chemical Equations

• Chemical equations consist of reactants and products.
• Reactants are the substances at the start of a reaction.
• Products are the result of a chemical reaction.

Symbols in Equations

• An arrow separates reactants from products.
• The + sign indicates "and."
• Suffixes like (s), (g), (l), and (aq) describe the physical state of a substance (solid, gas, liquid, aqueous solution respectively)
• Δ indicates that heat is added to the reaction.
• Pt or other similar notations indicate a catalyst.

Catalysts

• Catalysts speed up chemical reactions without being consumed.
• Enzymes are biological catalysts.

Law of Definite Proportions

• Atoms combine in specific ratios to create compounds with specific compositions.

Types of Chemical Reactions

• Combination (Synthesis): Two or more reactants combine to form a single product.

  • Example: Ca + O2 → CaO, SO3 + H2O → H2SO4

• Decomposition: A single reactant breaks down into two or more products.

  • Example: NaCl → Na + Cl2, CaCO3 → CaO + CO2

• Single Replacement: One element replaces another in a compound.

  • Example: K + NaCl → Na + KCl, F2 + LiCl → LiF + Cl2
  • Metals can replace each other and hydrogen in a similar reaction.
  • Example: K + HOH → KOH + H, Zn + HCL → ZnCl2 + H2

• Double Replacement: The ions of two compounds switch places to form two new compounds.

  • Example: AgNO3 + NaCl → AgCl + NaNO3, NaOH + HCl → NaCl + H2O

Combustion Reactions

• In combustion, oxygen combines with a substance to form carbon dioxide and water.
• An example is burning naphthalene: C10H8 + 12 O2 → 10 CO2 + 4 H2O

Acids and Bases

• Acids donate protons (H+) in solution.
• Examples: HCl → H+ + Cl−, H2SO4 → H+ + HSO4−
• Bases donate hydroxide ions (OH−) in solution.
  • Examples: NaOH → Na+ + OH−, KOH → K+ + OH−

Properties of Acids

• Acids taste sour and turn blue litmus paper red.
• Acids react with metals to release hydrogen gas.
• Acids react with carbonates/bicarbonates to produce CO2.
• Acids react with bases to produce salts and water.

Properties of Bases

• Bases taste bitter and feel soapy.
• Bases turn red litmus paper blue.
• Bases react with acids to form salts and water.

Modern Acid-Base Theory

• An acid is a substance capable of donating a proton.
• A base is a substance capable of accepting a proton.
  • Example: NH3 + H2O → NH4+ + OH−

Classification of Acids and Bases

• Strong acids and bases completely ionize in solution.
• Example: KOH → K+ + OH−
• Weak acids and bases only partially ionize.

Strong Acids

• HCl, HBr, HI, HClO3, HClO4, H2SO4, HNO3

Strong Bases

• NaOH, KOH, CsOH, Ca(OH)2

Dissociation Constant (K)

• K is the equilibrium constant for the dissociation of an acid or base.
• Ka is higher in strong acids.
• Kb is the dissociation constant of bases.

pH

• pH measures the concentration of hydrogen ions in a solution.
• The pH scale ranges from 0 to 14.

Measuring pH

• Litmus paper: changes color based on pH.
• pH paper: uses multiple dyes to indicate pH.
• pH meter: provides a precise pH measurement.

Salts

• Salts are ionic compounds with a positive ion (other than H+) and a negative ion (other than OH−).
• Different types of salts (e.g., Neutral, Acidic,Basic) result from different types of neutralization reactions.

Oxidation-Reduction Reactions

• Oxidation is loss of electrons or increase in valence.
• Reduction is gain of electrons or decrease in valence.
• Oxidation and reduction reactions always occur simultaneously.
• Oxidizing agents gain electrons; reducing agents lose electrons.